The disclosure relates to a lamp assembly, and more particularly to a ceramic metal halide (CMH) lamp assembly, that incorporates a reflector configured to provide multiple functions.
High intensity discharge lamps require high ignition voltages to break down a gap and initiate an arc between spaced electrodes. One example of a discharge lamp is a CMH lamp having an arc tube having first and second legs extending from axially opposite ends. Electrode assemblies are received in the respective legs and terminal ends of the electrode assemblies are spaced apart in the discharge chamber of the arc tube. Typically, the CMH lamp is received in a sealed shroud or capsule and includes a pinch or press seal region at one end in which molybdenum seals are mechanically and electrically interconnected at one end with respective inner leads that support the CMH light source and interconnect with the electrode assemblies, and at the other end with outer leads that mechanically and electrically connect with an associated power source.
These types of lamps require high ignition voltages to break down the gap and initiate an arc between the spaced electrodes. For example, an ignition pulse on the order of approximately 25 kV is required to start the lamp when the lamp is still hot; an ignition pulse on the order of 3 KV to 5 KV is required to start the lamp in normal condition (when the lamp is at room temperature). One conventional way to reduce starting difficulties is to fill the arc tube with radioactive krypton (Kr85) gas which requires a special license that regulates its use. Another manner of reducing the starting voltage aid is taught in commonly owned U.S. application Ser. No. 11/810,471, filed Jun. 6, 2007 (193334-1/GECZ 200793US01), the disclosure of which is expressly incorporated herein by reference in its entirety. The ignition voltage aid device of that disclosure is spaced closer to one of the electrodes than the arc gap dimension between the electrodes in order to significantly reduce the starting voltage for the lamp.
A CMH lamp has a very significant amount of backlight (approximately thirty percent (30%) of the emitted light) that is typically wasted. Generally, the wasted light is associated with that portion of the emitted light that is directed toward the pinch region.
In addition, overall reliability of the CMH lamp is dependent on and sensitive to the base end seal glass temperature. That is, the seal glass temperature of the base end (pinch region) is usually higher than the dome end of the surrounding capsule when the lamp is mounted at base up position. In addition, the capsule pinch temperature, especially for a higher wattage lamp, is very sensitive and thus adversely impacts on lamp reliability if exceeding 300° C.
Still another issue is the difficulty in keeping the arc tube centered inside of the capsule during manufacture. This is important to optimize beam performance since precisely locating the arc discharge relative to the lamp capsule directly effects light output and light intensity distribution, and likewise maximum beam performance is based in part on the location of arc tube relative to the capsule.
In addition, it is important to precisely align the arc tube within the capsule so that relatively even temperatures are created in the sidewall of the capsule.
Thus, a need exists for a lamp that overcomes one or more of these needs in a manner that is economical, efficient, and easy to implement.